"You said in the last debate that everyone should pay something," Cooper said at one point to Michele Bachmann. "Does that mean that you would raise taxes on the 47 percent of Americans who currently don't pay taxes?"

Wait, 47 percent of Americans don't pay taxes? That's not true.

It is true that 47 percent of Americans don't pay federal income taxes, because they get tax credits worth more than the amount of tax they owe. But income taxes are hardly the only federal taxes that people pay.

The average middle-income household pays almost 10 percent of its income in payroll taxes, as David Leonhardt of the New York Times wrote last year. Because payroll taxes are taxes on wages, they're not much different from income taxes. Payroll taxes are supposed to fund Social Security and Medicare, but for years the government has taken in more Social Security taxes than is needed to pay benefits, and has spent the money on other government programs.

That average household also pays about 1 percent of its income in gas and other federal excise taxes, and 1 percent of its income in corporate taxes, through the stocks it owns.